Essentials of Gregor Mendel Biology - Green River .Essentials of Biology ... 10.1 Mendel’s Laws

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  • Essentials of

    Biology

    Sylvia S. Mader

    Chapter 10

    Patterns of Inheritance

    Lecture Outline

    Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

    10.1 Mendels Laws

    Gregor Mendel Austrian monk

    Worked with pea plants in 1860s

    First person to analyze patterns of inheritance

    Deduced the fundamental principles of genetics.

    Mendel working in his Abbey Garden

    Studied garden peas

    Easily manipulated

    Can self-fertilize

    Many traits controlled by only one gene

    Figure 10.1 a. Flower structure

    ovary

    stigma

    anther

    Pollen grains containing sperm areproduced in the anther . When pollengrains are brushed onto the stigma,sperm fertilizes eggs in the ovary .Fertilized eggs are located in ovules,which develop into seeds.

    Figure 10.2 Garden pea anatomy & traits

    Used garden pea, Pisumsativa

    Easy to cultivate, short generation time

    Normally self-pollinate but can be cross-pollinated by hand

    Mendels Experimental Procedure

    Figure 10.2 (cont.)

    Cut away anthers.

    b. Cross pollination

    1

    2

    3

    Brush on pollen fromanother plant.

    The results of cross from aparent that produces round,yellow seeds parent thatproduces wrinkledyellow seeds.

    Used true-breeding varieties

    offspring were like the parent plants and each other

    Kept careful records of large number of experiments

    Used mathematical laws of probability to interpret results to develop his theory of inheritance

    Mendels Experimental Procedure

    Parents (P)

    Offspring (F1)

    Mendels Experimental Procedure

    Used true-breeding varieties

    offspring were like the parent plants and each other

    Kept careful records of large number of experiments

    Used mathematical laws of probability to interpret results to develop his theory of inheritance

  • Cross between true breeding long and short pea plants

    F1 Generation:

    All long

    Long Short

    P Generation

    Which phenotype is dominant?Recessive?

    F2 Phenotypic Ratio: of offspring are long (3 Long : 1 Short) of the offspring are short

    F2 Long Long Long Short

    Self-fertilization of F1

    How did Mendel Explain these results?

    Nucleus

    Long stemallele

    Short stemallele

    Purple flowerallele

    White flowerallele

    Flower color gene:

    A pair ofhomologous

    chromosomes

    A pair ofhomologous

    chromosomes

    Stem length gene:(a) Homozygous dominant

    (two matchingdominant alleles)

    (b) Heterozygous (nonmatchingalleles)

    Phenotype:Long Long Short

    Long stemallele

    Long stemallele

    A pair ofhomologouschromosomes

    Genotype:

    Long stemallele

    Short stemallele

    Short stemallele

    Short stemallele

    Genotype: (c) Homozygous recessive(two matching recessive alleles)

    Heterozygous plants

    Female Male

    Long Long

    (b) Alleles segregatein meiosis

    Genotypeof eggs

    Genotypeof sperm

    A Monhybrid Cross:

    Ll x Ll

    Genotype of Eggs Genotype of Sperm

    Alleles combine randomly during fertilization

    PunnettsquareGenotypic ratio:

    1 L L : 2 L l : 1 l l

    Phenotypic ratio:

    3 long : 1 short

  • Mendels Law of Segregation

    Alleles separate from each other during meiosis

    Results in gametes with one or the other allele, but never both

    Formation of gametes from a pre-gamete cell

    Genotype of Pre-gamete cell:

    meiosis

    Genotype of Gametes:

    A a

    Aa

    Genetic Terms

    1. Phenotype Vs. Genotypewhats the difference.

    2. What are Alleles?

    Alternate forms of a gene e.g.s?

    3. Where are the alleles of a gene located?

    4. How many alleles can a person inherit for any one trait?

    How many alleles are there in a population for a particular trait such as

    hair color?

    5. Whats the relationship between alleles and homologous chromosomes?

    6. Dominant vs. recessive alleleswhats the difference? E.g.s?

    7. How can you determine if an allele is dominant or recessive?

    Genotype: alleles individual receives at fertilization

    Homozygous: 2 identical alleles

    Homozygous dominant

    Homozygous recessive

    Heterozygous: 2 different alleles

    Phenotype: physical appearance of individual

    Determined by genotype and environmental factors

    Genotype vs. Phenotype

    Figure 10.5 Alleles on Homologous chromosomes Homologous Pair of Chromosomes with 3 linked genes

  • Family Pedigrees

    Shows the history

    of a trait in a

    family from one

    generation to

    another

    Allows

    researchers to

    determine if a

    phenotype is

    dominant or

    recessive

    Dominant vs. Recessive Phenotype

    Dominant Phenotype Recessive Phenotype

    Genotype PhenotypeRR = _____________________ ___________________

    Rr = _____________________ ___________________

    rr = _____________________ ___________________

    Allele Symbols:

    R = Tongue Roller

    r = Nonroller

    Types of Genotypes and their resulting Phenotypes

    Attached vs. Free Earlobes

    1. Due to a recessive or

    dominant allele?

    2. Sex-linked or

    Autosomal?

    3. Must examine a

    pedigree to answer

    these questions

    Marr Family Pedigree for Earlobe Attachment1. Which allele is

    dominant?

    Recessive?

    Is the allele for

    earlobe

    attachment sex-

    linked (X-

    linked) or

    autosomal?

    What are the

    genotypes of all

    family

    members?

    Marr Family Pedigree for Earlobe Attachment A family pedigree for Deafness

    Is deafness a dominant or recessive trait?

    How can you tell?

    Allele Symbols: D = _____________________ d=_______________________

    JoshuaLambert

    AbigailLinnell

    JohnEddy

    HepzibahDaggett

    AbigailLambert

    JonathanLambert

    ElizabethEddy

    Female Male

    Deaf

    Hearing

  • A family pedigree for Deafness

    Is deafness a dominant or recessive trait?

    How can you tell?

    Allele Symbols: D = _____________________ d=_______________________

    DdJoshuaLambert

    DdAbigailLinnell

    D_JohnEddy

    D_HepzibahDaggett

    D_AbigailLambert

    ddJonathanLambert

    DdElizabeth

    Eddy

    Dd Dd dd Dd Dd Dd dd

    Female Male

    Deaf

    Hearing

    Common Monogenic Human Traits

    Dominant Allele

    1. Free Earlobes

    2. Straight Thumb

    3. Long eyelashes

    4. Normal health

    5. Normal health

    6. Normal R.B.Cs

    7. Huntingtons Disease

    Recessive Allele

    Attached Earlobes

    Hitchhikers thumb

    Short eyelashes

    Cystic Fibrosis

    Tay-Sacs Disease

    Sickle cell anemia

    Normal Health

    Common Polygenic Human Traits

    Dominant

    1. Dark-colored hair

    2. Curly hair

    3. Dark eyes

    4. Hazel or green eyes

    5. Tall

    6. Dark skin

    Recessive

    Light-colored hair

    Straight hair

    Light eyes (blue or gray)

    Blue or gray eyes

    Short

    Light skin

    Common Sex-linked Recessive Human Traits: X-linked

    X-linked recessive traits

    Uncommon in femaleswhy?

    Father must have disease and mother must be a carrier for a daughter to have the disease.

    1. Color Vision

    XN = Normal color vision; Xn = Red/Green Colorblind

    2. Hemophilia:

    XN = Normal blood clotting; Xn = bleeder

    3. Duchenne Muscular Dystrophy

    XN = Normal muscles; Xn = muscular dystrophy

    Laws of Probabilityapplication to inheritance

    1. The results of one trial of a chance event do not affect

    the results of later trials of that same chance event

    E.g. Tossing of a coin, gender of children, etc.

    Laws of Probabilityapplication to inheritance

    2. The Multiplication Rule: The chance that two or more

    independent chance events will occur together is equal

    to the product of their chances occurring separately

    a. What are the chances of a couple having 9 girls?

    b. E.g. What are the chances of a couple having a boy with the

    following characteristics:

    Brown hair (3/4), Non-tongue roller (1/4), Blue eyes (1/4), Attached

    earlobes (1/4)

  • How to Solve Genetics Problems

    Sample Problem: Mom and dad are heterozygous for tongue rolling where tongue rolling is dominant to non-rolling. What is the chance that the couple will produce a girl that is a non-roller?

    Use the following steps as a general guide to solve this and other problems:

    1. Select a letter to represent the gene involved

    Use upper case for the dominant allele, lower case for the recessive allele.

    2. Write the genotypes of the parents.

    3. Determine all possible gametes for each parent.

    Alleles for a trait segregate into separate gametes during meiosis

    4. Determine the genotypes of the offspring.

    Make a Punnett square to represent all possible gamete combinations

    between the two parents

    5. Use the genotypes found in the Punnett Square to determine the possible

    phenotypes of the offspring to answer the question.

    Types of Genetics Problems

    Monohybrid Crosses

    Involve only one trait such as ??

    Sample Problem #1: True breeding parental pea plants were crossed to produce

    the F1 generation, below. The F1 generation was inbreed to produce an F2generation.

    a.) Which allele is dom